Parse deferred templates twice

Currently it is not possible to have a template file.epp ```puppet <%- | Stdlib::Port $port, String[1] $password, | %> port <%= $port %> password <%= $password %> ``` and run ```puppet file{'/tmp/junk': content => stdlib::deferrable_epp('module/file.epp', { 'port' => '1234', pass => Deferred('secrets::get',['mysecret'])}), } ``` since the deferred template substitution will fail: ``` Error: Failed to apply catalog: Evaluation Error: Resource type not found: Stdlib::Port (file: inlined-epp-text, line: 2, column: 3) ``` due to Stdlib::Port not being available on the agent node. This change now parses the EPP twice. The first pass will reduce the template to: ```puppet port = 1234 password <%= $password %> ``` and this simpler template will be passed in deferred mode. Note the original template type for password must accept the intermediate generated value of `<%= $password %>` which is typically case for a secret password.
puppetlabs · Apr 15, 2024 · 0c800b4 · 0c800b4
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diff --git a/REFERENCE.md b/REFERENCE.md
@@ -3173,18 +3173,38 @@ Type: Puppet Language
 This function returns either a rendered template or a deferred function to render at runtime.
 If any of the values in the variables hash are deferred, then the template will be deferred.
 
-Note: this function requires all parameters to be explicitly passed in. It cannot expect to
-use facts, class variables, and other variables in scope. This is because when deferred, we
-have to explicitly pass the entire scope to the client.
-
-#### `stdlib::deferrable_epp(String $template, Hash $variables)`
+Note: In the case where at least some of the values are deferred and preparse is `true` the template
+      is parsed twice:
+ The first parse will evalute any parameters in the template that do not have deferred values.
+ The second parse will run deferred and evaluate only the remaining deferred parameters. Consequently
+ any parameters to be deferred must accept a String[1] in original template so as to accept the value
+ "<%= $variable_with_deferred_value %>" on the first parse.
+
+ @param template template location - identical to epp function template location.
+ @param variables parameters to pass into the template - some of which may have deferred values.
+ @param preparse
+     If `true` the epp template will be parsed twice, once normally and then a second time deferred.
+     It may be nescessary to set `preparse` `false` when deferred values are somethig other than
+     a string
+
+#### `stdlib::deferrable_epp(String $template, Hash $variables, Boolean $preparse = true)`
 
 This function returns either a rendered template or a deferred function to render at runtime.
 If any of the values in the variables hash are deferred, then the template will be deferred.
 
-Note: this function requires all parameters to be explicitly passed in. It cannot expect to
-use facts, class variables, and other variables in scope. This is because when deferred, we
-have to explicitly pass the entire scope to the client.
+Note: In the case where at least some of the values are deferred and preparse is `true` the template
+      is parsed twice:
+ The first parse will evalute any parameters in the template that do not have deferred values.
+ The second parse will run deferred and evaluate only the remaining deferred parameters. Consequently
+ any parameters to be deferred must accept a String[1] in original template so as to accept the value
+ "<%= $variable_with_deferred_value %>" on the first parse.
+
+ @param template template location - identical to epp function template location.
+ @param variables parameters to pass into the template - some of which may have deferred values.
+ @param preparse
+     If `true` the epp template will be parsed twice, once normally and then a second time deferred.
+     It may be nescessary to set `preparse` `false` when deferred values are somethig other than
+     a string
 
 Returns: `Variant[String, Sensitive[String], Deferred]`
 
@@ -3200,6 +3220,12 @@ Data type: `Hash`
 
 
 
+##### `preparse`
+
+Data type: `Boolean`
+
+
+
 ### <a name="stdlib--end_with"></a>`stdlib::end_with`
 
 Type: Ruby 4.x API

diff --git a/functions/deferrable_epp.pp b/functions/deferrable_epp.pp
@@ -1,15 +1,39 @@
 # This function returns either a rendered template or a deferred function to render at runtime.
 # If any of the values in the variables hash are deferred, then the template will be deferred.
 #
-# Note: this function requires all parameters to be explicitly passed in. It cannot expect to
-# use facts, class variables, and other variables in scope. This is because when deferred, we
-# have to explicitly pass the entire scope to the client.
+# Note: In the case where at least some of the values are deferred and preparse is `true` the template
+#       is parsed twice:
+#  The first parse will evalute any parameters in the template that do not have deferred values.
+#  The second parse will run deferred and evaluate only the remaining deferred parameters. Consequently
+#  any parameters to be deferred must accept a String[1] in original template so as to accept the value
+#  "<%= $variable_with_deferred_value %>" on the first parse.
 #
-function stdlib::deferrable_epp(String $template, Hash $variables) >> Variant[String, Sensitive[String], Deferred] {
+#  @param template template location - identical to epp function template location.
+#  @param variables parameters to pass into the template - some of which may have deferred values.
+#  @param preparse
+#      If `true` the epp template will be parsed twice, once normally and then a second time deferred.
+#      It may be nescessary to set `preparse` `false` when deferred values are somethig other than
+#      a string
+#
+function stdlib::deferrable_epp(String $template, Hash $variables, Boolean $preparse = true) >> Variant[String, Sensitive[String], Deferred] {
   if $variables.stdlib::nested_values.any |$value| { $value.is_a(Deferred) } {
+    if $preparse {
+      $_variables_escaped = $variables.map | $_var , $_value | {
+        if $_value.is_a(Deferred) {
+          { $_var => "<%= \$${_var} %>" }
+        } else {
+          { $_var => $_value }
+        }
+      }.reduce | $_memo, $_kv | { $_memo + $_kv }
+
+      $_template = inline_epp(find_template($template).file,$_variables_escaped)
+    } else {
+      $_template = find_template($template).file
+    }
+
     Deferred(
       'inline_epp',
-      [find_template($template).file, $variables],
+      [$_template, $variables],
     )
   }
   else {

diff --git a/spec/functions/stdlib_deferrable_epp_spec.rb b/spec/functions/stdlib_deferrable_epp_spec.rb
@@ -24,8 +24,37 @@
 
     it {
       foo = Puppet::Pops::Types::TypeFactory.deferred.create('join', [1, 2, 3])
-      # This kind_of matcher requires https://github.com/puppetlabs/rspec-puppet/pull/24
-      expect(subject).to run.with_params('mymod/template.epp', { 'foo' => foo }) # .and_return(kind_of Puppet::Pops::Types::PuppetObject)
+      expect(subject).to run.with_params('mymod/template.epp', { 'foo' => foo }).and_return(kind_of(Puppet::Pops::Types::PuppetObject))
+    }
+  end
+
+  context 'defers rendering with mixed deferred and undeferred input' do
+    let(:pre_condition) do
+      <<~END
+        function epp($str, $data) { fail("should not have invoked epp()") }
+        function find_template($str) { return "path" }
+        function file($path) { return "foo: <%= foo %>, bar: <%= bar %>" }
+      END
+    end
+
+    it {
+      foo = Puppet::Pops::Types::TypeFactory.deferred.create('join', [1, 2, 3])
+      expect(subject).to run.with_params('mymod/template.epp', { 'foo' => foo, 'bar' => 'xyz' }).and_return(kind_of(Puppet::Pops::Types::PuppetObject))
+    }
+  end
+
+  context 'defers rendering with mixed deferred and undeferred input and preparse false' do
+    let(:pre_condition) do
+      <<~END
+        function epp($str, $data) { fail("should not have invoked epp()") }
+        function find_template($str) { return "path" }
+        function file($path) { return "foo: <%= foo %>, bar: <%= bar %>" }
+      END
+    end
+
+    it {
+      foo = Puppet::Pops::Types::TypeFactory.deferred.create('join', [1, 2, 3])
+      expect(subject).to run.with_params('mymod/template.epp', { 'foo' => foo, 'bar' => 'xyz' }, false).and_return(kind_of(Puppet::Pops::Types::PuppetObject))
     }
   end
 end